1. Field of the Invention
The present invention relates to the field of semiconductor devices, more particularly to the field of semiconductor memory devices, e.g. capacitor structures. More particularly the present invention relates to a method to selectively form Ru and/or RuO2 as an oxygen diffusion barrier in such memory devices, and to memory devices provided with such Ru-based diffusion barrier.
2. Technical Background
For future MIM (metal-insulator-metal) capacitor devices, Ru and RuO2 are the most interesting candidates to replace current TiN bottom and top electrodes. It has been suggested that RuO2 is more likely a candidate thanks to RuO2 reduction to Ru releasing O2 into the capacitor dielectric to help suppress capacitor leakages at the operation voltage through high-k material such as e.g. SrTiO3.
In the choice of RuO2 film formation, however, converting Ru to RuO2 by oxidation could generate some rough surface morphology which in turn degrades leakage current. On top thereof, CVD Ru or an as-deposited RuO2 process could oxidize the substrate, including the plug/barrier metal thus making a higher contact resistance. Up to now, TiN has been used most widely as oxidation barrier, but with the new Ru or RuO2 as bottom and/or top electrodes, stronger oxidation barriers than TiN are needed in order to prevent oxidation of underlying metals during metal or metal oxide deposition in an oxidizing ambient.